96 z24 cavalier idle problem 2.4

[msca]

when you first start the car it spits and sputters a little for a few min then it starts runing good until it warms completly up. then it starts that spit and sputtering again at idle.the car runs good while driving just when its idling.ive changed every sensor on the car. checked fuel pressure.some guy said check for vacum leaks.could not find any.but found out the car idles good when i disconnect the vacum line that goes from the throttle body threw the fire wall to the heater controls that blows my air threw my vents.are they somthing that im over looking. run out of things to check thanks mike

[J-Ri]

Originally Posted by msca

but found out the car idles good when i disconnect the vacum line that goes from the throttle body threw the fire wall to the heater controls that blows my air threw my vents.

That shouldn't be... There's nothing in the vacuum portion of the HVAC system that would affect how the engine runs. Check the vacuum hose that goes to the MAP sensor. They deteriorate for some reason and will leak. The only thing I can think of is that the MAP hose is leaking and the sensor is reading less vacuum than there is, and disconnecting the HVAC vacuum drops the vacuum just enough. Did you check for codes and check the spark plugs?

[msca]

Originally Posted by J-Ri

That shouldn't be... There's nothing in the vacuum portion of the HVAC system that would affect how the engine runs. Check the vacuum hose that goes to the MAP sensor. They deteriorate for some reason and will leak. The only thing I can think of is that the MAP hose is leaking and the sensor is reading less vacuum than there is, and disconnecting the HVAC vacuum drops the vacuum just enough. Did you check for codes and check the spark plugs?

i will check the hose that goes to the map sensor. today i was checking the vacum hose that i was disconnecting. and it didnt change it at all . i put new plugs in about 2weeks ago. and i put the cheap ones in. do you think that would have something to do with it. dont they call for a certain kind of plug. no engine light. but i took it to a garage and they hooked some kind of a computer up and it said gas recircalation .so he said try the egr sensor .so i did. and nothing.runs same way . before i changed all the sensors .it was running real bad you could smell gas fumes strong .then the engine light would throw a random misfire .then i put all the sensors. new gas new plugs coils and it dont have a bad gas oder no more but still has that little loping sound just not as bad .thanks

[J-Ri]

Plugs could possibly cause it... personally, I would get the AC Delcos specified for your car and see if that takes care of it. Try the simple things first.

[RahX]

Definitely check the MAP sensor hose, its a small elbow that I've seen crack on hundreds of cars. Also, AC Delco plugs are the only way to go for GM, NEVER EVER use a Bosch spark plug of any sort for anything. Those engines were pretty good about the coils arcing through that crazy cover thing too, might check for carbon tracking on the plug boots and the plastic coil cover thingy. You can replace the plastic separate if I remember right.

[msca]

well i replaced the hose to the map sensor. bought new plugs.didnt help at all.found out the intake gasket was blowed.fix that. and its still doing the same thing.i replaced the coil housing just a few weeks ago.checked the gasket between the trottle body and intake.and its ok.sounds like what ever controls the fuel delivery is the problem.you can smell gas strong when its running.and when ever it starts this loping sound you can hear something kick in and try to make it run right for about a second then it goes right back to that loping sound .could it be the fuel pump.probaly have to take it to the dealer

[J-Ri]

You said the fuel pressure was good, that means the pump is not bad. If the pump was bad, it wouldn't run bad at idle and fine when you're driving. Since it ran better when you removed that vacuum line, wiggle any wires you may have touched while removing the hose. May have an open or short inside a harness. You didn't say if you checked for codes... are there any? If you haven't checked codes, do that first, then if none, disconnect sensors one at a time (with the key off. Won't run at all with the crank sensor unplugged, so skip that one) and if it starts running better with one unplugged, that's the circuit with the problem (will usually be the sensor or it's input). This will set codes, so check them first so you know that you caused all the codes. Also make sure that the MAP sensor is getting vacuum from the manifold, may have some carbon buildup in the manifold that's blocking it.

[msca]

Originally Posted by J-Ri

You said the fuel pressure was good, that means the pump is not bad. If the pump was bad, it wouldn't run bad at idle and fine when you're driving. Since it ran better when you removed that vacuum line, wiggle any wires you may have touched while removing the hose. May have an open or short inside a harness. You didn't say if you checked for codes... are there any? If you haven't checked codes, do that first, then if none, disconnect sensors one at a time (with the key off. Won't run at all with the crank sensor unplugged, so skip that one) and if it starts running better with one unplugged, that's the circuit with the problem (will usually be the sensor or it's input). This will set codes, so check them first so you know that you caused all the codes. Also make sure that the MAP sensor is getting vacuum from the manifold, may have some carbon buildup in the manifold that's blocking it.

yes it does set a code p0300 random misfire detected.i took it to the dealer this morning and they work on it all day.and they said the injectors oil rings were bad.so they put new ones on.and they said they couldnt find any thing else wrong.but its still doing the same thing.never helped a bit.i checked the map sensor hose.ive got vacum.but like you said it could not have enough.i will go check for carbon build up in the trottle body.ill check those sensor to.thanks

[manicmechanix]

Since you did all that work on it and I'm going to assume that the pressure regulator's not leaking and fuel pressure is good, there's no vacuum leaks, and the engine mechanical condition is good, all the sensors are working fine and the dealer checked the fuel injectors. There's a chance that there's corrosion at your PCM and connectors. Some 95-96's had this problem. There was even a recall. If your car is affected and hasn't had the recall done, the dealer should have caught that, but they don't catch everything. Check your PCM and PCM connectors under the passenger wheel well for corrosion and/or ask a dealer about checking your car for the recall.

[msca]

Originally Posted by manicmechanix

Since you did all that work on it and I'm going to assume that the pressure regulator's not leaking and fuel pressure is good, there's no vacuum leaks, and the engine mechanical condition is good, all the sensors are working fine and the dealer checked the fuel injectors. There's a chance that there's corrosion at your PCM and connectors. Some 95-96's had this problem. There was even a recall. If your car is affected and hasn't had the recall done, the dealer should have caught that, but they don't catch everything. Check your PCM and PCM connectors under the passenger wheel well for corrosion and/or ask a dealer about checking your car for the recall.

i put a regulator on didnt help .when i bought this car it was running this way. i checked everything that i could.then after working all day trying to figure it out .it quit and wouldnt start back so i thought the computer was bad .so i went and got one.plug it up and nothing so i took it to the dealer because they said it had to be programed.and they said to put my original computer back in the car.so i did. thay work on it and said it needed the coil housing.i told them to fix it.i went and pick it up and still the same thing.i have noticed white smoke alot coming from the tell pipe but it dont smell like antfreeze it smells like gas .it clears up but after you lit it cool down it will put out white smoke again .like its flooding .do you think the head gasket could be leaking a little.i checked the fuel pressure on start up.and it seems to be strong 50 to 60 but i cant check it when its running.first thing i done was check compression .i had 180 on 3 cyl 210 on the other. dealer said that was fine.car runs good while driving.just on idle and idles good sometimes .dealer told me that they drove it all over the place and that it was running good.i took it to them 3 times and plus what ive worked on it. and still got the same miss that it had when i bought it.thanks

[manicmechanix]

Originally Posted by msca

i put a regulator on didnt help .when i bought this car it was running this way. i checked everything that i could.then after working all day trying to figure it out .it quit and wouldnt start back so i thought the computer was bad .so i went and got one.plug it up and nothing so i took it to the dealer because they said it had to be programed.and they said to put my original computer back in the car.so i did. thay work on it and said it needed the coil housing.i told them to fix it.i went and pick it up and still the same thing.i have noticed white smoke alot coming from the tell pipe but it dont smell like antfreeze it smells like gas .it clears up but after you lit it cool down it will put out white smoke again .like its flooding .do you think the head gasket could be leaking a little.i checked the fuel pressure on start up.and it seems to be strong 50 to 60 but i cant check it when its running.first thing i done was check compression .i had 180 on 3 cyl 210 on the other. dealer said that was fine.car runs good while driving.just on idle and idles good sometimes .dealer told me that they drove it all over the place and that it was running good.i took it to them 3 times and plus what ive worked on it. and still got the same miss that it had when i bought it.thanks

By rough idle do you mean the engine rpm goes up and down. Doe s it do this in neutral? So there was no corrosion at the PCM?

I don't know what to tell you. You say you checked and replaced practically everything but the engine its self. Something is being overlooked. Usually on these models when you checked things out and it still runs rough and no check engine light, it's the fuel injectors. This can be checked with an injector drop test and injector coil test. What doesn't make sense though is if your injectors are clogged or acting up that you'd smell fuel unless the injectors were leaking or the fuel pressure is too high.

Fuel pressure should be 41-47 not 50 or 60. why couldn't you check it when it's running? If you have 50-60 then you have a regulator problem or your fuel return line is kinked. So if you say "fuel pressure is good at 50-60psi", no one can make sense of the diagnostics because that's not good. There are several things that could cause the problem but it doesn't sound like this car is being properly diagnosed even by the dealer. The dealer should've found the problem. But going off what you've said, I'd double check the fuel pressure and the injectors.

[RahX]

Have you checked the O2 sensor at all?

[J-Ri]

Sounds like he's got a fuel pressure gauge that dead-heads the pressure line. You'll need to get an adapter hose that "T"s into the fuel line and let you check pressure off the "T" so you see what's actually going into the engine. Pumps can have good pressure with no flow, but drop very low as soon as you let any fuel flow, but probably not a fuel issue. You also can't dead-head the line like that, because you're not seeing what the pressure regulator is doing or if there's a problem with the return line. I agree with the fuel injectors.

O2 sensors wouldn't make it run bad when it's cold.

[msca]

Originally Posted by manicmechanix

By rough idle do you mean the engine rpm goes up and down. Doe s it do this in neutral? So there was no corrosion at the PCM?

I don't know what to tell you. You say you checked and replaced practically everything but the engine its self. Something is being overlooked. Usually on these models when you checked things out and it still runs rough and no check engine light, it's the fuel injectors. This can be checked with an injector drop test and injector coil test. What doesn't make sense though is if your injectors are clogged or acting up that you'd smell fuel unless the injectors were leaking or the fuel pressure is too high.

Fuel pressure should be 41-47 not 50 or 60. why couldn't you check it when it's running? If you have 50-60 then you have a regulator problem or your fuel return line is kinked. So if you say "fuel pressure is good at 50-60psi", no one can make sense of the diagnostics because that's not good. There are several things that could cause the problem but it doesn't sound like this car is being properly diagnosed even by the dealer. The dealer should've found the problem. But going off what you've said, I'd double check the fuel pressure and the injectors.

with car in neutral.engine rpm goes up and down.at start up. after it warms up a little it runs perfect idles good then after it gets fully warmed up it starts that spit and splutter sound like its flooding.they were no corrosion at the pcm.but some one had been working on the computer before.they had put black caulk all around the computer like they was trying to keep water out of it .thats one reason why i thought the computer was bad.but when i took it to the dealer to have the new computer programed they said put the original computer back in the car.thats when they said it needed the coil housing. replaced all 4 injectors from another car and didnt change it a bit.the engine light comes on p0300 random misfire.and when i seen the fuel pressure go to 50 or 60 i just figured that was good.i would have had to cut the metal line to to splice it all together to check it running.i just didnt think the fuel pump had anything to do with it.but any way i sold the
car today and i lit it go cheap so they could take it to there dealer and try to figure out whats going on.i told her to lit me no what was wrong.ill lit you all no.thanks

[manicmechanix]

Originally Posted by msca

with car in neutral.engine rpm goes up and down.at start up. after it warms up a little it runs perfect idles good then after it gets fully warmed up it starts that spit and splutter sound like its flooding.they were no corrosion at the pcm.but some one had been working on the computer before.they had put black caulk all around the computer like they was trying to keep water out of it .thats one reason why i thought the computer was bad.but when i took it to the dealer to have the new computer programed they said put the original computer back in the car.thats when they said it needed the coil housing. replaced all 4 injectors from another car and didnt change it a bit.the engine light comes on p0300 random misfire.and when i seen the fuel pressure go to 50 or 60 i just figured that was good.i would have had to cut the metal line to to splice it all together to check it running.i just didnt think the fuel pump had anything to do with it.but any way i sold the
car today and i lit it go cheap so they could take it to there dealer and try to figure out whats going on.i told her to lit me no what was wrong.ill lit you all no.thanks

I see now. The engine didn't have a test port and you were getting dead head pressure. You would've needed a T fitting like J-ri said. It sounds like someone was trying to complete the PCM corrosion recall I mentioned. that was one of the steps to put RTV around the PCM. Maybe whoever worked before replaced the PCM and didn't do the crank sensor relearn procedure. Or maybe your car was never a recall model and the RTV was put on at the factory. But switching injectors didn't help either makes it seem like there might've been a hard to find wiring problem or problem at the PCM. Sounds like you really had a tough problem to diagnosis. Sorry to hear you had to let it go cheap after doing all that work. If you ever find out if the dealer figures out the problem let us know.